Daily Practice Problems

Class 11 Physics

Laws of Motion

Class 11 Physics

Laws of Motion

**Question 1.**

State Newton’s three laws of motion.

**Question 2.**

Give an expression for Newton’s second law of motion.

**Question 3.**

What do you understand by Impulse?

**Question 4.**

Give symbol, units and dimensions for static and kinetic friction.

**Question 5.**

What do you understand by friction?

**Question 6.**

A stone of mass 0.50 kg tied to the end of a string is whirled round in a circle of radius 2.0 m with a speed of 30 rev/min in a horizontal plane. What is the tension in the string? What is the maximum speed with which the stone can be whirled around if the string can withstand a maximum tension of 300N?

**Question 7.**

A batsman deflects a ball by an angle of 30^{0} without changing its initial speed which is equal to 72 km/h. What is the impulse imparted to the ball? (Mass of the ball 0.20 kg).

**Question 8.**

Eight five-rupee coins are put on top of each other on a table. Each coin has a mass m. Give the magnitude and direction of

- The force on the fifth coin (counted from the bottom) due to all the coins on its top,
- The reaction of the 4
^{th}coin on the 5^{th}coin.

**Question 9.**

A shell of mass 0.025 kg is fired by a gun of mass 200 kg. If the muzzle speed of the shell is 75 m/s. What is the recoil speed of the gun?

**Question 10.**

Two masses 5 kg and 10 kg are connected at the two ends of a light inextensible string that goes over a frictionless pulley. Find the acceleration of the masses, and the tension in the string when the masses are released.** **

**Question 11.**

A truck starts from rest and accelerates uniformly at 3.0 m/s^{2}. At t = 12 s, a stone is dropped by a girl standing on the top of the truck (8m high from the ground). What are the (a) velocity, and (b) acceleration of the stone at t = 13s.

**Question 12.**

A constant retarding force of 40N is applied to a body of mass 15 kg moving initially with a speed of 10 m/s. How long does the body take to stop?

**Question 13.**

Give the statement for “Law of conservation of Momentum”.

**Question 14.**

A circular racetrack of radius 500m is banked at an angle of 22.5^{0} . If the coefficient of friction between the wheels of a race-car and the road is 0.15. What is the, (a) optimum speed of the race-car to avoid wear and tear on its tyres, and (b) maximum permissible speed to avoid slipping?

**Question 15.**

Determine the maximum acceleration of the train in which a box lying on its floor will remain stationary, given that the co-efficient of static friction between the box and the train’s floor is 0.2.

**Question 16.**

What is the unit and dimension of “Impulse”?

**Question 17.**

Give the magnitude and direction of the net force acting on a stone of mass 0.5 kg.

- Just after it is dropped from the window of a stationary car.
- Just after it is dropped from the window of a car accelerating with 2 m/s
^{2}.

**Question 18.**

Two billiard balls each of mass 0.08 kg moving in opposite directions with speed 5 m/s collide and rebound with the same speed. What is the impulse imparted to each ball due to the other?

**Question 19.**

A stream of water flowing horizontally with a speed of 12 m/s gushes out of a tube of cross-sectional area 2×10^{-2 }m^{2} and hits a vertical wall nearby. What is the force exerted on the wall by the impart of water, assuming it does not rebound?

**Question 20.**

A bob of mass 0.2 kg hung from the ceiling of a room by a string 4 m long is set into oscillation. The speed of the bob at its mean position is 1.5 m/s. What is the trajectory of the bob if the string is cut, when the bob is (a) at one of its extreme positions, and (b) at its mean position?

**********